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Evaluation of Insecticides for the Economic Control of Root Weevils in Blueberry 2002

Evaluation of Insecticides for the Economic Control of Root Weevils in Blueberry, 2002

L. K. Tanigoshi and J. R. Bergen
Washington State University
Vancouver Research and Extension Unit
Vancouver, WA 98665-9752
tanigosh@wsu.edu, bergenj@coopext.cahe.wsu.edu

The black vine (Fig. 1), Otiorhynchus sulcatus, and strawberry root (Fig. 2), O. ovatus,weevils pose serious economic injury during the 1-2 year non-bearing period the immature plant is maturing in the field. Field observations indicate the economic threshold for 2 to 3 year-old bare root or container grown plants is one root weevil larvacapable of girdling the cambium of large roots (Fig. 3) and killing the plant (Fig. 4). Black vine weevils are readily managed in container-grown nurseries in the US and Europe by incorporating bifenthrin (Talstar® 0.2 G) into potting media to kill their larvae. We tested Talstar 0.2 G at 15 and 25 ppm as a pot media mix (50% peat moss, 50% pumice) (Fig. 5) and at 12 ppm as a top dressing (sawdust) incorporation and two rates of the soil-applied formulation of thiamethoxam (Platinum® 2SC) as a drench and an untreated check. Treatments were replicated 10 times and infested on27-28 March. Talstar was incorporated in the soil on 25 March and as a top dressing on 3 April. The two drenchrates of Platinum were applied onto the infested pots on 4 April. Each replicated contained 10late instar black vine weevils that were placed in 2-3 inch holes around a 3 year-old plant and then covered with potting mix (Figs. 6-7). After one month the blueberry plants were top at the soil surface and each pot covered with a square pane of clear glass. The final evaluation occurred on 30 May to compared adult emergence for all treatments with the untreated check.

Compared with the untreated check, all treatments and soil application methods were significantly different (Table 1). Both rates of Talstar applied as a soil incorporate into potting media used in containerized planting could easily translate to the planting technique used in commercial plantings. We imagine that a moist pot media mix containing Talstar would be incorporated in the planting hole. In addition an organic mulch top dressing would further provide root weevil suppression at 12 ppm along with providing weed suppression, soil moisture and increase organic matter. Platinum applied as a transplant drench performed similar to the Talstar soil incorporation. We will expand potting trials next year to further verify theexcellent data were obtained this year. Perhaps the non-bearing period for maturing blueberry plants is ideal for the application for a widely accepted tactic to prevent girdling and root browsing by root weevil larvae.

 

Table 1.

Treatment Rate Applications Mean adults/pot1

Platinum 2SC 5 ft.oz/acre Drench 0.3c
Platinum 2SC 8 fl.oz/acre Drench 0.5c
Talstar GC 15 ppm Pot Media Mix 0.0c
Talstar GC 25 ppm Pot Media Mix 0.0c
Talstar GC 12 ppm Top Dressing 2.2b
Untreated Check 8.8a

Used 100 BVW late instar larva for each treatment. Means within column followed by the same letter are not significantly different
(Tukey HSD test, P<0.05).
1Infested 27-28 March, evaluated 30 May 2002.